Tubular lamp manufacture



Oct. 19, 1954 J. B. YODER TUBULAR LAMP IMNUFA CTU'RE Filed Sept. 29. 1951 lnven tor: doe Yoder,

His A t torneg.

Patented Oct. 19, 1954 UNITED STATES TUBULAR LAMP MANUFACTURE Joe B. Yoder, Mayfield Heights, Ohio, assignor to General Electric Company, a corporation of New York Application September 29, 1951, Serial No. 248,997

4 Claims.

The present invention relates to electric lamps and more particularly the invention relates to electric lamps of the elongated tubular type shaped to a substantially closed configuration with the lam ends juxtaposed and facing each other.

Fluorescent discharge lamps of this type are commercially available at present in the form of circles and are mass produced by machines which shape the tubular glass envelope thereof into the desired circular shape after the luminescent powder has been applied to the inner surface of the envelope and the electrodes have been mounted in its ends. After the envelope has been so shaped it is exhausted and filled with a starting gas at a few mm. pressure together with a measured small amount of mercury. The envelope is then sealed off from the exhaust system and is ready for basing to complete the lamp.

Occasionally it has been found that lamps completed except for the basing have had to be discarded because the spacing of the lamp ends was not within the tolerances of the bases to be applied. 'Io discard such otherwise completed and operative lamps would add considerably to the cost of producing commercial lamps.

Using bases of different sizes on the defective lamps was not practical due to the variety of defects existing. For example, in some lamps the end spacing was too small, in others too large, and in some the ends were offset from each other. Further, the use of bases of different sizes is not possible in lamps designed for standard fixtures.

Due to the great pressure differential between the inside and the outside of the envelope of such semi-finished lamps it was not possible to reheat the envelope to the softening temperature of the glass and reshape it as was done in shaping the lamp envelope prior to exhaust thereof, because the exhausted envelope would of course collapse if heated to such temperature.

I have discovered, however, that the glass envelopes of such exhausted lamps may be reshaped to the extent required to obtain the necessary spacing between and relative positioning of the lamp ends without collapsing the lamp envelope to the end that the cost of manufacture of such lamps is substantially reduced by eliminating shrinkage from this cause.

In accordance with my discovery a circumferential zone of the exhausted tubular glass envelope between its ends is uniformly heated to slightly above the annealing point but substantially below the softening point of the glass after which the ends of the lamps envelope are manipulated into the proper position for basing. The heat treatment of the circumferential zone of the envelope is continued only as long as required first to uniformly heat the glass of the envelope to slightly above the annealing temperature of the glass and then to manipulate the lamp ends into proper position. With lam envelopes as presently manufactured, a heating period of approximately three minutes before manipulating the ends of the lamp envelope is sufficient.

A heat source capable of accurate control and positioning is of course essential for uniformly heating the glass in the circumferential zone of the tubular envelope. and for this purpose an elec trio radiant heater is referred.

In the drawing accompanying and forming part of this specification a novel apparatus useful for carrying out the new method of the invention is shown in Figs. 1 and 2 in which Fig. l is a top plan view of the apparatus with an unbased lamp mounted thereon and Fig. 2 is a side elevational view of the apparatus shown in Fig. 1; Fig. 3 is a fragmentary, top plan view of a based lamp on a slightly enlarged scale.

Referring to Figs. 1 and 2 of the drawing, the apparatus comprises an electric stove l fixedly mounted on a base plate 2 having four adjustable legs 3 near its corners for levelling purposes. The top of the stove i, provided with a handle 5 for lifting purposes, is hinged to the body portion 6 of the stove as shown at I and is supported in its raised and backwardly tilted position by the stop 3 mounted on the base plate 2.

The top 1 of the stove I when closed defines with the body portion 6 thereof an open-ended tubular oven 9 extending through the stove and parallel to the base 2. Both parts 4 and 6 are provided with wire heater coils It arranged in parallel segments extending longitudinally of the oven. Insulated current lead wires H attached to conventional terminals [2 on the parts 4 and 6 of the stove are provided to connect the heater elements It, which are connected in series by insulated lead wire l3, across the terminals of a suitable power source.

A circular lamp M is held in proper position with a portion thereof to be heated extending through the oven 9 in the stove I by an adjustable, tilted, flat platform i5 mounted on the base. The platform i5 is supported in its tilted position by a pair of legs l6 fixedly mounted on the base 2 and in opposing positions with respect to the stove I. The angle to which the platform [5 is tilted may be changed by adjusting the nuts H on the screw-threaded legs I6 if found necessary for obtaining uniform heating of the lamp envelope portion in the oven 9.

The platform it has a cut-out portion 18 to fit around the stove l and is provided with a pair of fixed studs i9 having sleeves 28 and so positioned with respect to the oven 9 in the stove that a lamp M'not too badly deformed is properly positioned in the oven when resting on the platform 15 and against the sleeves 20 on the studs I9. The sleeves 20 are provided to allow for variations in lamp shades and one or both of the sleeves may be removed from the studs it when 3 necessary for properly positioning a particular lamp in the oven 9.

A gauge block 2| resting on the platform [5 is utilized by the operator in adjusting the lamp ends 22 to the proper spacing within the tolerances of the base to be mounted on the lamp ends and bridge the gap between the ends 22.

At present circular fluorescent discharge lamps are made of a lead glass having an annealing temperature of 428 C. and a softening temperature of 626 C. In properly positioning the ends 22 of such lamps by the method and apparatus described above, the stove l is adjusted to raise the portion of the glass envelope it surrounds to a temperature of about 450 C. within about three minutes.

In order to compensate for convection currents within the stove oven 9 which tend to defeat uniform heating of the glass throughout the circumference of the lamp envelope, the platform I5 is so adjusted with respect to the diameter of the tubular lamp envelope that the longitudinal axis of the lamp envelope is ofiset downwardly from the longitudinal axis of the oven 9 in the stove l in order to bring the lower portion of the envelope closer to the radiant heater I0 than the top portion thereof. With circular lamps having an outer diameter of 12 inches and a tube outer diameter of 1 inches a downward oifset of /4 inch is effective with an oven 9 having an inner diameter of 2% inches and a length of 4 inches.

At the end of the preliminary heating period, the envelope portions near the ends 22 are grasped by the hands of the operator and, with the heating continued, are manipulated until the proper setting of the ends 22 is obtained. The gauge block 2! aids the eye of the operator in determining when the lamp ends have been brought into properly spaced relative positions for basing. The ends 22 remain in such position when removed from the apparatus and the heated portion of the lamp envelope has cooled to room temperature. The lamp then may be provided with a base in the usual manner to complete the lamp as shown in Fig. 3 in which a base 23 bearing contact pins 24 is shown mounted on the lamp ends 22 and bridging the space therebetween. The base 23 is split longitudinally as indicated at 25 and the two parts thereof are held together on the lamp ends by a bolt 26 through the base 23, as is well known.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of attaching a single base of predetermined dimensions to both ends of a sealed highly exaeuated tubularglass electric discharge lamp envelope having a substantially closed configuration with its ends juxtaposed but outside the tolerances of the base, the glass of said envelope having a softening temperature approximately 200 C. higher than its annealing temperature, which comprises the steps of first heating the glass of said tubular evacuated glass envelope to a temperature of not more than about 25 C. above its annealing temperature in a circumferential zone sufficiently narrow to preclude collapse of the tubular envelope at the aforesaid temperature, then manipulating the ends of the envelope into relative positions within the tolerances of the base while maintaining said zone at said temperature, discontinuing the heating when said ends have been so positioned and thereafter attaching the base to the ends of the envelope.

2. The method of attaching a single base of predetermined dimensions to both ends of a sealed highly evacuated tubular glass envelope having a circular configuration with its ends juxtaposed but outside the tolerances of the base, the glass of said envelope having a softening temperature approximately 200 C. higher than its annealing temperature, which comprises the steps of first heating the glass of said tubular evacuated glass envelope to a temperature not more than about 25 C. above its annealing temperature in a circumferential zone sufficiently narrow to preclude collapse of the tubular envelope at the aforesaid temperature, said zone being spaced an appreciable distance from the ends of the envelope, then manipulating the ends of the envelope into relative positions within the tolerances of the base while maintaining said zone at said temperature, discontinuing the heating when said ends have been so positioned and thereafter attaching the base to the ends of the envelope.

3. The method of permanently readjusting the end positioning of a highly evacuated, doubleended hermetically sealed tubular envelope of glass having a softening temperature of the order of 200 C. higher than its annealing temperature without collapsing the walls of said envelope, which comprises the steps of heating the glass of said tubular evacuated envelope to rapidly raise its temperature to not more than about 25 C. above its annealing temperature in a circumferential zone sufficiently narrowto preclude collapse of the tubular envelope at the aforesaid temperature, continuing the heating of said zone while manipulating the ends of the envelope into predetermined relative positions and then discontinuing the heating and the manipulation.

4. The method of attaching a single base of predetermined dimensions to both ends of a hermetically sealed, highly evacuated tubular glass envelope having a substantially closed configuration with its ends juxtaposed but outside the tolerances of the base, the glass of said envelope having a softening temperature of approximately 626 C. and an annealing temperature of about 428 C., which comprises the steps of first heating the glass of said tubular evacuated glass envelope to a temperature of about 450 C. within about three minutes in a circumferential zone sufficiently narrow to preclude collapse of the tubular envelope at the aforesaid temperature, manipulating the ends of the envelope into relativepositions within the tolerances of the base while maintaining said zone at said temperature and then discontinuing the heating of said zone upon attaining the proper positioning of the said envelope ends and thereafter attaching the base to said ends.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,135,775 Walker Nov. 8, 1938 2,351,530 McGowan June 13, 1944 2,359,500 White Oct. 3, 1944 2,407,878 Greetham Sept. 17, 1946 2,427,722 Greiner Sept. 23, 1947 FOREIGN PATENTS Number Country Date 154,609 Germany Oct. 4, 1904 510,505 Germany Oct. 22, 1930 539,291 Germany Nov. 24, 1931 

